The present invention relates to a solenoid head driving circuit of a printer, more particularly to a solenoid head driving circuit capable of preventing current flowing through the solenoid from undesirably increasing.
Referring to FIG. 1, a structure of a printing head of a wire dot matrix printer conventionally used will be described hereinafter. In a casing 82 of a printing head 81, a large number of comb shaped teeth 83, for example, 24, in FIG. 1, in a particular pitch are disposed in circumferential. On the comb shaped teeth 83, a solenoid coil 84 is wound, and thus, a solenoid is structured. At the end of an armature 85 which is driven by the solenoid, printing pins 86 are disposed.
FIG. 2A is a conceptual schematic showing positional relationship among the solenoids 1 through 24 on a typical solenoid head. In the meantime, a semi-conductor element comprising a package in which a plurality of transistor chips are housed is called "transistor array" hereinafter. FIG. 2B is a schematic showing conventionally used connections between the solenoids 1 through 24 and transistor arrays 70a through 70f. Conventionally, as shown in FIG. 2B, when the transistor arrays 70a through 70f are connected to the solenoids 1 through 24, for example, one transistor array 70a is connected to four solenoids 2, 4, 6, and 8 which are adjacently disposed as shown in FIG. 2A.
However, when printing pins which are adjacently disposed are simultaneously driven by driving the solenoids adjacently disposed, as shown in FIG. 3, an amount of current which flows through in one solenoid is proportional to the number of adjacently disposed solenoids "S" which are driven at a time due to magnetic effect. In other words, a magnet field which is generated by the current flowing through a certain solenoid generates current flowing the solenoid adjacently located with the certain solenoid in the same direction of the current having been flowed through the adjacent solenoid, and then, the current flowing the adjacent solenoid is increased. Thus, in the conventional structure where the four solenoids adjacently disposed are connected to transistors of one transistor array, when only the four solenoids are always driven so as to execute a printing operation, an amount of current which flows through each of solenoids respectively increase. The total amount of current which flows through the four solenoids becomes larger than the 4 times of current which flows through a solenoid when one printing pin is driven. Thus, even if no duty limit is applied because of low printing duty, an excessive load is applied to one transistor array, resulting in problems with respect to safety and life of the product.